4,198 research outputs found
Calculated elastic and electronic properties of MgB at high pressures
The effect of high pressure on structural and electronic properties of the
novel superconductor \MB has been calculated using the full-potential
linearized augmented-plane-wave method. Despite the layered crystal structure
of \MB nearly isotropic compression (bulk modulus GPa) is found
with only a 1.2% decrease of the ratio at 10 GPa. The effect of pressure
on the critical temperature has been estimated on the basis of BCS theory and
good agreement with experimental data is found. Our results suggest that it is
a combination of increasing phonon frequency and decreasing electronic density
of states at the Fermi level which leads to the observed decrease of the
critical temperature under pressure.Comment: 10 pages, 3 figures (EPS), Elsevier LaTeX. More detailed analysis of
the pressure dependence of Tc; results unchanged. Manuscript accepted for
publication in Solid State Commu
Forecasting for day-ahead offshore maintenance scheduling under uncertainty
Offshore wind farm maintenance operations are complex and dangerous, and as such are subject to strict safety constraints. In addition, crew and vessels must be scheduled in advance for both planned and reactive maintenance operations. Meteorological forecasts on many time-scales are used to inform scheduling decisions, but are imperfect. Short-term maintenance scheduling is therefore a problem of decision-making under uncertainty. This paper proposes a probabilistic approach to the short-term scheduling problem based on a cost-loss model for individual maintenance missions, and probabilistic forecasts of appropriate access windows. This approach is found to increase the utilisation of possible access windows compared to using deterministic decision rules. The impact of forecasting on the availability and operational costs of oshore wind is then examined using a Monte Carlo-based cost model. This has quantified the impact on availability and revenue performance under a range of site conditions
Pair-wise decoherence in coupled spin qubit networks
Experiments involving phase coherent dynamics of networks of spins, such as
echo experiments, will only work if decoherence can be suppressed. We show
here, by analyzing the particular example of a crystalline network of Fe8
molecules, that most decoherence typically comes from pairwise interactions
(particularly dipolar interactions) between the spins, which cause `correlated
errors'. However at very low T these are strongly suppressed. These results
have important implications for the design of quantum information processing
systems using electronic spins.Comment: 4 pages, 4 figures. Final PRL versio
Ice Sheet Elevation Change in West Antarctica From KaâBand Satellite Radar Altimetry
Satellite altimetry has been used to track changes in ice sheet elevation using a series of Kuâband radars in orbit since the late 1970s. Here, we produce an assessment of higherâfrequency Kaâband satellite radar altimetry for the same purpose, using SARAL/AltiKa measurements recorded over West Antarctica. AltiKa elevations are 3.8 ± 0.5 and 2.5 ± 0.1 m higher than those determined from airborne laser altimetry and CryoSatâ2, respectively, likely due to the instruments' coarser footprint in the sloping coastal margins. However, AltiKa rates of elevation change computed between 2013 and 2019 are within 0.6 ± 2.4 and 0.1 ± 0.1 cm/year of airborne laser and CryoSatâ2, respectively, indicating that trends in radar penetration are negligible. The fastâflowing trunks of the Pine Island and Thwaites Glaciers thinned by 117 ± 10 and 100 ± 20 cm/year, respectively, amounting to a 9% reduction and a 43% increase relative to the 2000s
Wave height forecasting to improve off-shore access and maintenance scheduling
This paper presents research into modelling and predicting wave heights based on historical data. Wave height is one of the key criteria for allowing access to off-shore wind turbines for maintenance. Better tools for predicting wave height will allow more accurate identification of suitable âweather windowsâ in which access vessels can be dispatched to site. This in turn improves the ability to schedule maintenance, reducing costs related to vessel dispatch and recall due to unexpected wave patterns. The paper outlines the data available for wave height modelling. Through data mining, different modelling approaches are identified and compared. The advantages and disadvantages of each approach, and their accuracies for a given site implementation, are discussed
Numerical Study of Competing Spin-Glass and Ferromagnetic Order
Two and three dimensional random Ising models with a Gaussian distribution of
couplings with variance and non-vanishing mean value are studied
using the zero-temperature domain-wall renormalization group (DWRG). The DWRG
trajectories in the () plane after rescaling can be collapsed on two
curves: one for and other for . In the first case
the DWRG flows are toward the ferromagnetic fixed point both in two and three
dimensions while in the second case flows are towards a paramagnetic fixed
point and spin-glass fixed point in two and three dimensions respectively. No
evidence for an extra phase is found.Comment: a bit more data is taken, 5 pages, 4 eps figures included, to appear
in PR
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